Method of forming a molded pulse oximeter sensor

ABSTRACT

A pulse oximeter sensor apparatus which is sealed against liquid penetration during its formation by overmolding, and methods for overmolding. The pulse oximeter sensor apparatus disclosed comprises a preform first section, oximeter sensor components, and an overmolded second section bonded to the preform first section during the overmolding process to form a liquid resistant seal comprising a mechanical bond of overlapping elements.

This is a continuation of application Ser. No. 08/267,849 filed on Jun.29, 1994, now U.S. Pat. No. 5,425,360, which is a continuation of Ser.No. 07/919,220 filed on Jul. 24, 1992, now abandoned.

BACKGROUND OF THE INVENTION

The field of the present invention is sensor apparatus for pulseoximetry.

Pulse oximetry provides a means of non-invasively measuring oxygensaturation of arterial blood for purposes of monitoring and evaluatingthe physical condition of a patient under medical care and to avoidpatient hypoxemia. Pulse oximetry functions by positioning a pulsatingarterial vascular bed (such as that in a patient's finger or ear lobe)between a two-wavelength light source and a detector. The pulsatingvascular bed, by expanding and relaxing, creates a change in the amountof light passing through at each wavelength. Oxyhemoglobin and reducedhemoglobin differ in their light absorption characteristics. The varyingamounts of light from the light source passing through the vascular bedare received by the detector as a waveform, whose signal is processedelectronically by a pulse oximeter into a measurement of arterialhemoglobin oxygen saturation. Such oximeters are described, e.g., inU.S. Pat. No. 4,824,242, which is incorporated herein by reference.

A sensor apparatus, containing the light source, the detector, andconnecting wiring or cables, is used to position the light source anddetector components in proper relation to each other at an appropriatebody site. For example, the light source may be positioned on one sideof a patient's finger, with the detector positioned directly oppositethe light source on the other side of the finger. Cables and wiringconnect the light source and detector at the patient site, and transmitthe waveform signal to the oximeter for processing. The light source,the detector, and their connecting wires have typically been secured toa support which facilitates proper placement of the light source anddetector in relation to each other and at the desired site on thepatient. For example, the light source, detector, and connecting cableshave been attached to a flexible wrap material, which is wrapped aroundand temporarily secured to a body site, such as a finger. Such a sensorapparatus generally is a single use, disposable item due to its directcontact with the patient. A drawback of such a disposable oximetersensor apparatus is its relatively high cost per use.

Alternately, sensor components (including the light source, detector,and connecting wires) have been mounted and sealed into, for example, amolded shell which can be disinfected and reused in multipleapplications and among different patients. However, such a reusableoximeter sensor apparatus must be relatively durable to withstandmultiple attachments, and the sensor components must be sealed withinthe molded shell so that application of liquid disinfectant to thesurface of the shell by wiping or immersion will not result in moisturereaching and damaging the sensor components. Further, the moldingprocess must be accomplished without the use of excess or prolonged hightemperature which would damage the sensor components.

As a result, existing reusable oximeter sensors have been relativelycostly since their manufacture is labor and/or time intensive. Forexample, such reusable sensors have been manufactured by first moldingtwo shell halves, enclosing the sensor components between the halves inproper position, and then gluing the halves together to seal outmoisture, a time and labor intensive process.

Alternatively, reusable oximeter sensors have been manufacturedutilizing a silicone overmolding process, in which the sensor componentsare positioned within a first premolded silicone half shell, and thenencased and sealed as silicone is injected in an overmolding step tocomplete the molded shell. Due to the properties of the silicone used,the two portions of the completed molded shell seal to each other.However, the cycle time for this overmolding operation is typically25-40 minutes, depending on the specific type of silicone and its curingtemperature. The curing temperature must be kept low, resulting in therelatively long cure time, since excess heat will destroy the cable andoptical components which comprise the active sensor components. Further,given such long cycle times, each base mold can produce only relativelyfew molded sensors per day, requiring large capital expenditures formultiple base molds or tools to achieve significant daily volumeproduction of sensors.

SUMMARY OF THE INVENTION

The present invention is directed to oximeter sensors which can bedisinfected and reused. The oximeter sensors of the present inventionare simultaneously formed and sealed utilizing overmolding withoutrequiring lengthy cure times, and enclose sensing components. Theoximeter sensor comprises a preformed first section and an overmoldedsecond section which is sealed to the first section utilizing a moldedmechanical bond of overlapping elements.

Accordingly, it is an object of the present invention to provide a lowcost, reusable oximeter sensor utilizing an overmolding process.

A further object of the present invention is to provide a method forovermolding a reusable, low cost oximeter sensor.

Other and further objects and advantages of the present invention willbe evident hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a preferred embodiment of the present sensor apparatusinvention. FIG 1a shows the back side of the apparatus.

FIG. 1b shows the front or patient side of the apparatus.

FIG. 1c shows a cross-sectional view of FIG. 1b taken along line 1c--1c.

FIG. 2 shows the interior surface of the premolded preform firstsection.

FIG. 2a shows a cross-sectional view of FIG. 2 taken along line 2a--2a.

FIG. 3 shows a cross-sectional view of the premolded preform firstsection of FIG. 2 taken along line 3--3.

FIG. 4a shows the sensor light source window.

FIG. 4b shows a cross-sectional view of FIG. 4a taken along line 4b--4b.

FIG. 5a shows the sensor detector window.

FIG. 5b shows a cross-sectional view of FIG. 5a taken along line 5b--5b.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Turning in detail to the drawings, FIGS. 1a, 1b, and 1c illustrate amolded pulse oximeter sensor apparatus 10 of the present invention. Asshown in FIG. 1c, the active sensing components comprising the lightsource ceramic 11, detector ceramic 12, and connecting wires 11a arecontained within the completed sensor apparatus 10. Cable 12a connectsthese active elements to a pulse oximeter. Cable 12a may extend from thesensor apparatus 10 in various directions and orientations. The lightsource 11 and detector 12 are mounted into pre-molded clearpolyvinylchloride (PVC) window compartments 13 and 14 such that thelight source and detector each physically interlock into theirrespective window compartments. These window compartments can be moldedby those skilled in the art using PVC materials such as, e.g., MaclinVM-3270 clear.

Window compartments 13 and 14 are mounted into a premolded preform firstsection 15. These window compartments are shown in FIGS. 4a, 4b, 5a, and5b. The premolded preform first section 15 may be molded, usingtechniques known to those of skill in the art, from an appropriate 38durometer medical grade PVC material, such as, e.g., Maclin Apex-3500R40 white. The premolded preform first section 15 contains a cavity 16for the light source window compartment 13 and a cavity 17 for thedetector window compartment 14. Each cavity is molded to have lockingfeatures for positive mounting and sealing of the windows into thepremolded perform first section 15. The features of the window cavities16 and 17 are shown in FIGS. 2 and 3. The insertion of both the lightsource 11 and detector 12 into their respective window compartments 13and 14, and the insertion of window compartments 13 and 14 into theirrespective cavities 16 and 17 in the premolded preform first section 15is facilitated by the fact that both the PVC windows and the preformfirst section are fairly compliant and permit stretching of theinterlocking features during insertion. Once inserted, the compliant PVCmaterial returns to its initial molded shape. The window compartments 13and 14 extend to the exterior surface or patient side 15a of the preformfirst section 15, as shown in FIGS. 1b and 1c.

Wires 11a connecting the light source 11 are mounted into wire guides 18that locate and position the wires 11a along the interior surface of thepreform first section 15 for proper orientation and alignment of thewires during the overmolding operation. The preform first section 15employs the above mentioned wire guides 18 which transverse the distancebetween the detector 11 and the light source 12 ceramics to preventmovement of or damage to the wires 11a during the overmolding operation.These wire guides 18 may comprise grooves, or raised ridges, or both,along the interior surface of the preform first section

In an alternate embodiment, the light source 11, detector 12, andconnecting wires 11a may instead be contained in a one-piece Kapton flexcircuit formed from high strength, high temperature plastic material.This flex circuit is positioned along the interior surface of thepreform first section 15, and the light source and detector portions ofthe flex circuit again interlock into pre-molded clear PVC windowcompartments which are mounted into the preform first section 15.

The requirements of signal strength for the light source 11 may causeproduction of excess heat, which could burn a patient. The mounting ofthe light source 11 within its window compartment 13 provides a bufferbetween the light source 11 and the patient contact point, protectingthe patient from excess heat, as well as sealing the light sourceceramic 11 from the patient side 15a of the preform first section 15.Similarly the window compartment 14 for the detector 12 is utilized forsealing and protecting the detector ceramic 12, as well as providing anadditional patient buffer against electrosurgical grounding discharges.The window compartment 14 also eliminates any need for secondaryoperations of backfilling the cavity 17, as would otherwise be requiredto secure and seal the detector 12 into the preform first section 15.

In the overmolding operation, the overmolded second section 19 is formedby injection molding, preferably using the same PVC material as is usedto form the preform first section 15. The preform first section 15 andsensor components are properly positioned and placed into a base mold.Overmolding material (PVC) is injected to form the overmolded secondsection 19 and to enclose the sensor components between the preform andovermolded sections and to bond these two sections together, forming thecompleted oximeter sensor apparatus 10. During the overmolding step, thecable 12a is also surrounded by the injected PVC material at the pointthe cable 12a exits the molded sensor apparatus. In the preferredembodiment, the major mold base is designed so that it accommodatesinsertion of a separate mold system, called coffin molds. These coffinmolds hold the preform assembly, which includes the preform firstsection 15 fitted with window compartments 13 and 14 containing thelight source 11 and detector 12, and connecting wires 11a and 12a, allsecured into proper position. The coffin mold holds and retains thepreform assembly in proper alignment, and allows insertion and removalof the preform assembly into and out of the main mold base forovermolding. Use of coffin molds thereby protects the sensor componentsfrom high base mold temperatures which could damage the components. Useof coffin molds also facilitates rapid loading of the base mold andremoval of the completed overmolded sensor apparatus 10.

In order to provide a seal which is resistant to penetration by liquidsbetween the preform first section 15 and the overmolded second section19, without the need for the high temperatures required to achieve atotal fusion bond of the two PVC surfaces, a mechanical bond is formedduring the overmolding process. To accomplish this, in the preferredembodiment the preform first section 15 is provided with protuberancesin the form of dovetail-shaped ribbing 20 extending from the majority ofthe periphery of the interior surface of the preform first section 15.Thus, when the overmolding operation is performed, the new injectionmolding (PVC) material flows around the dovetail-shaped ribbing 20 andphysically forms a mechanical bond between the elements of theovermolded second section 19 which abut and overlap the ribbing elements20 of the preform first section 15. As a result, a liquid-resistant sealor bond between the preform first section 15 and the overmolded secondsection 19 is formed during overmolding, sealing the sensor componentswithin the resulting sensor apparatus 10. This seal, as formed duringovermolding, prevents moisture from liquids used to disinfect (by wipingor immersion) the sensor apparatus 10 between patients or applicationsfrom contacting the sensor components enclosed within the sensorapparatus 10.

In an effort to further reduce costs, the mold for the preform firstsection 15 may be designed into the main mold base, such that thepreforms are molded at the same time that the overmolding operationtakes place.

While embodiments and applications of this invention have been shown anddescribed, it would be apparent to those skilled in the art that manymore modifications are possible without departing from the inventiveconcepts herein. The invention, therefore, is not to be restrictedexcept in the spirit of the appended claims.

What is claimed is:
 1. A method of forming a molded pulse oximeter sensor apparatus utilizing an overmolding step, comprising:supplying a preform first section having an interior surface and an exterior surface; securing oximeter sensing components in a fixed configuration to said interior surface of said preform first section so that the position of said sensing components will be maintained during overmolding; and utilizing injection molding to overmold a second section which is bonded to said preform first section such that said sensing components are enclosed between said preform first section and said overmolded second section, and wherein the bond between said preform first section and said overmolded second section at their peripheries comprises a mechanical bond of overlapping elements.
 2. The method of claim 1 wherein said mechanical bond of overlapping elements comprises protuberances extending from the surface of said preform first section along its periphery, said protuberances having a shape such that said protuberances are wider at a point more distant from the surface of said preform first section than at a point closer to the surface of said preform first section, and wherein said overmolded second section is formed surrounding said protuberances.
 3. The method of claim 2 wherein said protuberances have a dovetail shape such that the narrowest portion of the dovetail is closer than its widest portion to the surface of said preform first section from which said protuberances extend.
 4. The method of claim 2 wherein said protuberances extend perpendicularly from the surface of said preform first section.
 5. The method of claim 1 wherein said bond formed during overmolding between said preform first section and said overmolded second section is resistant to penetration by liquid.
 6. The method of claim 1 wherein said bond formed during overmolding between said preform first section and said overmolded second section prevents liquid from penetrating the bond and contacting the sensing components positioned between said first and second sections.
 7. The method of claim 1 wherein said oximeter sensing components comprise a light source, a detector, and connecting wires.
 8. The method of claim 1 further comprising supplying window compartments which interlock into position in cavities contained in said preform first section and which extend to the exterior surface of said preform first section, and into which window compartments the light source and detector sensing components are secured.
 9. The method of claim 8 wherein said window compartments form a seal with said preform first section which is resistant to penetration by liquid.
 10. The method of claim 1 wherein coffin molds are utilized to hold said preform first section and oximeter sensing components during the overmolding step, and wherein said coffin mold is inserted into the base mold during overmolding. 